A conventional undervoltage circuit breaker with these features is described in U.S. Pat. No. 4,890,184.
Although undervoltage circuit breakers are used in electrical installations to prevent damage to loads whose operating voltage must not fall below a predetermined level, it may nevertheless be desirable not to have each voltage reduction lead to shutdown of the load. In particular, it may be desirable to disregard brief interruptions or brief dropping of the voltage below a minimum. This is accomplished by the above-mentioned delay in triggering. The small space provided in compact low-voltage circuit breakers, for example, for installation of an undervoltage circuit breaker does not, however, usually make it possible to accommodate capacitors with a suitably large capacitance in addition to the electromagnet and the components of the driver circuit. Likewise, it is not usually possible to accommodate suitable capacitors outside the switching device because the installation space provided for the power switch in switchgear or control cabinets is dimensioned only for the power switch. Therefore, the delay that can be achieved is limited to relatively small values.
One of the objects of the present invention is to create a predetermined required triggering delay when there is an undervoltage, using a smallest possible capacitance.